The present invention relates to an inverter circuit which comprises a first and a second switching means which are connected, in an electrical path, in series to one another and parallel to a DC link capacitor and the control connections of which are each connected to a pulse control device. The inverter circuit also comprises an output and two inputs, which are each electrically-conductively connected to a pole of the DC link capacitor and can each be connected to a pole of an energy store, as well as a voltage limitation element which is electrically-conductively connected to the electrical path by a first connection between the two switching means and to the control connection of the second switching means by a second connection.
Inverter circuits, also simply referred to as inverters or alternating-current converters, are one of the most important constituents in electrical drives, in particular in electrical drives which are supplied with a DC voltage. In the German patent publication DE 3415011 A1, such an inverter circuit is denoted/disclosed there as an inverter device. More precisely stated, an inverter device comprising semiconductor current control elements is described in said German patent publication DE 3415011 A1. In said inverter circuit, a parallel circuit comprising a current limiting circuit and a diode is connected in series to each of the semiconductor current control elements in order to prevent an excessive current from flowing through the same.
The German patent publication DE 10 2009 014 704 A1 furthermore discloses a drive system and a method for operating a drive system, which comprises an electric motor, a power inverter and an energy store, wherein the electric motor can be supplied by the power inverter and wherein a controllable current from a switch can be supplied to at least one stator winding of the electric motor, said current being supplied from an electrical energy source that is different from the energy store.
In addition, the German patent publication DE 60 2004 004 669 T2 relates to a control device for a multi-phase and reversible starter generator which is connected to a battery and an on-board power supply and, on the one hand, comprises a bridge having switches in the form of power transistors and, on the other hand, an electronic control and monitoring unit comprising actuating devices for actuating the gates of the power transistors. FIG. 1 shows a further inverter circuit 80 of the prior art in a state, where said inverter circuit is connected to an energy store 90 and a load 100. The inverter circuit 80 comprises a first and a second switching means 1, 2 which are connected, in an electrical path 10, in series to one another and parallel to a DC link capacitor 20 and the control connections 3 of which are each connected to a pulse control device 5, which, in this example, of an inverter circuit 80 of the prior art is only depicted for the lower, second switching means 2. The inverter circuit 80 also comprises an output 9, which, in this example, is electrically-conductively connected to the electrical path 10 between the first and the second switching means 1, 2, and two inputs 11, 12 which are each electrically-conductively connected to a pole of the DC link capacitor 20 and in each case to a pole of an energy store 90. The inverter circuit of the prior art furthermore comprises a voltage limitation element 30 which is electrically-conductively connected to the electrical path 10 by a first connection thereof between the two switching means 1, 2 and to the control connection 3 of the second switching means 2 by a second connection thereof. In this example, the voltage limitation element 30 is designed as a Zener diode 30.
The voltage limitation element 30 is used to break down voltage spikes occurring at the output 9, i.e. between the first and the second switching means 1, 2 in the electrical path 10. If a voltage spike occurs at the output 9 or, respectively, between the first and the second switching means 1, 2 in the electrical path 10, for example due to an interrupted current flow in the load 100, the second switching means 2 is then actuated when the breakdown voltage of the Zener diode has been exceeded in order to facilitate a certain current flow and to break down the voltage spike. A control circuit 70 is additionally located in the inverter circuit 80, said control circuit limiting the voltage at the output 9 via an intervention at the control connection 3 of the second switching means 2. The dynamics of such an intervention are, however, small and cannot correct short surge voltage spikes. It is furthermore a problem with the inverter circuit 80 depicted in FIG. 1 that the voltage at the output 9 or, respectively, between the first and second switching means 1, 2 in the electrical path 10 can drift with increasing age when temperature fluctuations occur and due to the tolerances of the components. Hence, a variation around +/−50 V is, for example, possible at a design voltage of 400 V. The voltage applied to the DC link capacitor 20 can therefore also be greater than the design voltage, according to which the DC link capacitor 20 as well as the other components have to be dimensioned.